Nickel-hydrogen cells are available which comprise a negative electrode prepared from a hydrogen absorbing alloy which reversibly absorbs or desorbs hydrogen. Nickel-hydrogen cells are known as cells having a high capacity, giving a high output and also high in energy density per unit volume and per unit weight.
It is required that nickel-hydrogen cells be given a still higher capacity. As a primary factor impeding increases in capacity, there is the problem that during charging, especially during rapid charging or overcharging, a side reaction of the charge reaction occurs at the hydrogen absorbing alloy electrode to produce hydrogen gas, increasing the internal pressure of the cell.
To solve this problem, there is a need to cause the electrode to efficiently absorb the hydrogen in its interior. Accordingly, a hydrogen absorbing alloy electrode is known which is prepared from a hydrogen absorbing alloy powder subjected to a water-repellent treatment and thereby held out of direct contact with the electrolyte within the cell to effect a promoted gas-solid reaction between the hydrogen and the alloy powder.
When the alloy is treated for water repellency, the reaction between the hydrogen (gas phase) and the hydrogen absorbing alloy (solid phase) is promoted, but there arises the problem of impeding the cell reaction of the alloy through the electrolyte (liquid phase).
JP-A No. 162353/1992 therefore discloses a hydrogen absorbing alloy electrode which is prepared from two kinds of hydrogen absorbing alloy powders only one of which is subjected to a water-repellent treatment, whereby the electrode is given improved hydrogen gas absorbing ability.
The disclosed electrode nevertheless has the problem of being unsatisfactory in discharge characteristics at low temperatures since the two kinds of hydrogen absorbing alloys have the same stoichiometric ratio represented by AB.sub.5 (in atomic ratio).
An object of the present invention is to provide a hydrogen absorbing alloy electrode which is given further improved hydrogen gas absorbing ability and improved low-temperature discharge characteristics.